Full mesh optical interconnect

ABSTRACT

The present invention comprises a full mesh optical interconnect with redundant power distribution conductors. The interconnect in a preferred form of backplane provides a set of optical transmission guides and power distribution conductors such that each circuit board assembly within a system can directly transmit data to any and all other circuit boards within the system and such that each circuit board assembly is provided with power from a centralized source such as the −48v battery subsystem provided by most central switching offices. A modified interconnect in the form of a midplane is disclosed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to full mesh optical interconnectsincluding optical midplanes and backplanes for interconnectingelectronic systems particularly communications systems. The opticalinterconnect provides dedicated high bandwidth connections between eachcircuit board assembly and every other circuit board assembly within agiven electronics system.

[0002] Communication systems, especially those developed for scaleablehigh bandwidth systems, require interconnects more particularly referredto herein as backplanes in order to interconnect circuit boardassemblies comprising the system. Backplanes are the ordinary means ofproviding such interconnection. In practice, ordinary electricalbackplanes normally require a multitude of electrical connections foreach circuit board in the system, thus reducing the reliability of thesystem. Additionally, each circuit board in the system must share thecommunications paths on electrical backplanes so that only a fraction ofthe overall bandwidth is available to each circuit board. Furthermorethe sharing of resources is detrimental to system reliability in that afailure on one circuit board assembly is likely reduce the utility ofthe shared paths for all circuit boards. In communications systems whereredundant subsystems are more commonly used, ordinary backplanes provideredundancy only at great expense. Finally, electrical backplanes arewell known to be a source of electromagnetic emissions and crosstalkwhereas an optical transmission guide emits no measurable radiation inthe RF spectrum and there is no capacitive or magnetic coupling.

[0003] Other optical interconnection systems have been devised, howevermost are either costly systems that comprise a number of expensiveoptical elements like embedded fiber-optic cable and related connectors,mirrors, turning mirrors, holographic elements, graded index materialsor lenses. The prior art also contains a few examples of inventions thatattempt to provide the necessary function of perpendicular routings ofsignals from one circuit board assembly to the next but do so byutilizing unproven, undefined or costly manufacturing processes orrequire fundamental changes to the construction of the associatedprinted circuit board assemblies. In yet other inventions, opticalinterconnection methods rely on a line of sight connection, the bondingof fiber-optic cables to integrated circuit waveguides or connections ona single printed circuit board assembly. In the case of electricalbackplanes and more than one optical interconnect invention, broadcastsystems are typically employed that share the utility of the providedcommunications path. Broadcast systems create contention for resourcesas well as interference between communication channels.

[0004] Another common problem with backplane and midplane designs is thenotion of upgradeability. Backplanes have been historically designed soas not to contain any active components since they represent a singlepoint of failure for the system that employs them. This is true of thepresent invention which provides interconnects without activecomponents.

[0005] The present invention also provides a simple means to upgrade thecapacity of a given backplane in the field simply by attachingadditional waveguide plates to the backplane which are available toserve new circuit board assemblies added to the system while existingcircuit board assemblies continue to perform their functions. This isanother important quality of the present invention since it can be usedto prevent the need for what is known in the art as a forklift upgrade.

[0006] So, there is a need for an alternative to electrical backplanescapable of providing inexpensive scaleable bandwidth, reliableoperation, a minimum of electrical connections, dedicated communicationspaths, reduced electromagnetic emissions and has the ability to beupgraded in the field.

[0007] The present invention provides a full mesh optical interconnectin which each circuit board assembly is assigned a dedicated opticaltransmission path to every other circuit board assembly in acommunications system. The only electrical connections necessary foreach circuit board assembly are electrical power connections.

SUMMARY OF THE INVENTION

[0008] The present invention provides full mesh optical interconnectsincluding backplanes and midplanes having redundant power transmissionconductors and a set of optical transmission guides for accommodating aset of circuit board assemblies forming part of an electronic system.Each circuit board assembly is provided with electrical power throughthe redundant power transmission conductors from a centralized sourcesuch as the −48v battery subsystem provided by many central switchingoffices. The optical transmission guides enable direct transmission ofdata from each circuit board assembly within a system to any and allother circuit boards within the system.

[0009] In a preferred embodiment of the invention, individual plates ordiscs embody optical transmission guides with an assembly or stack ofthe discs comprising a backplane. The stack of discs is bound togetherby means of metallic conductors that also provide a means for powertransmission. Circuit board assemblies in a system are connected to thebackplane in such manner that each circuit board receives power frommetallic conductors, and communicates through dedicated opticaltransmission guides with every other circuit board assembly in thesystem. Full mesh is the operating condition in which each circuit boardassembly communicates over dedicated paths with every other circuitboard assembly in a system.

[0010] In specific embodiments of (n) circuit board assemblies,((n)×(n−1)) optical transmission guides are required. For the simplecase of one circuit board, no transmission guides are required. For twocircuit board assemblies, two transmission guides are required: one totransmit from the first assembly to the second assembly, and one totransmit from the second assembly to the first assembly. For simplicity,the equation describing the number of transmission guides can be dividedby two to account for the generalized requirement for bi-directionaltransmission. Thus for example, in a system comprising eight circuitboard assemblies, ((8×7)/(2)) or twenty-eight transmission guide pairsare required and each circuit board assembly would be connected to seventransmission guide pairs so that it could communicate directly with eachof its circuit board neighbors.

[0011] In a preferred embodiment of the invention, each circuit boardassembly in the system has (n−1) optical interfaces arranged along anedge of the circuit board, with each optical interface comprising both atransmitter and a receiver. In addition, each circuit board assembly inthe system has a redundant number of electrical contacts along the sameedge to obtain the required electrical power to perform its function.Redundant electrical contacts are provided to enhance the reliability ofthe power distribution means.

[0012] The present invention provides a full mesh optical interconnectin several embodiments without expensive optical elements, resorting tounproven or costly manufacturing processes, fundamental changes to theconstruction of related circuit board assemblies, line of sight opticalconnections, bonding fiber-optic cables to integrated circuitwaveguides, or strictly limiting upgrades to forklift upgrades.

[0013] Specific examples are included in the following description forpurposes of clarity, but various details can be changed within the scopeof the present invention.

OBJECTS OF THE INVENTION

[0014] An object of the invention is to provide a full mesh opticalinterconnect for electronic systems enabling high bandwidth dedicatedconnections between each circuit board assembly and every other circuitboard assembly in the system.

[0015] Another object of the invention is to provide opticalinterconnects having optical transmission guides with each guide beingin optical isolation from all optical guides in the backplane.

[0016] Another object of the invention is to provide opticalinterconnects having scaleable means for increasing mesh size as thenumber of circuit boards is increased thereby adding dedicated pairs ofoptical transmission guides between circuit boards.

[0017] Another object of the invention is to improve reliability ofelectronic systems.

[0018] Another object of the invention is to reduce the number ofelectrical connections required for each circuit board in the system.

[0019] Another object of the invention is to reduce electromagneticemissions of communications systems.

[0020] An object of the invention is to provide a full mesh opticalbackplane enabling dedicated connections between each circuit boardassembly and every other circuit board assembly in the system in aneconomical manner.

[0021] Another object of the invention is to provide mating structuresfor optical waveguides that allow for abutment of an additional set ofwaveguides for extending an optical path directly to a circuit boardassembly.

[0022] Another object of the invention is to minimize length of opticalpaths and thereby minimize transmission delay in optical signals.

[0023] Another object of the invention is to provide electricalisolation of the circuit board assemblies in a system.

[0024] Another object of the invention is to minimize surface area ofoptical interconnects such as backplanes thereby to minimize air flowrestrictions and improve heat dissipation.

[0025] Other and further objects of the invention will become apparentwith an understanding of the following detailed description of theinvention or upon employment of the invention in practice.

DESCRIPTION OF THE DRAWING

[0026] A preferred embodiment of the invention has been chosen fordetailed description to enable those having ordinary skill in the art towhich the invention appertains to readily understand how to constructand use the invention and is shown in the accompanying drawing in which:

[0027]FIG. 1 is a perspective view of the preferred embodiment of a fullmesh optical backplane according to the invention.

[0028]FIG. 2 is a perspective view of a circuit board assembly designedfor use with the optical backplane of FIG. 1.

[0029]FIG. 3 is a table illustrating the assignment of opticaltransmission guides to the optical waveguide plates forming part of theoptical backplane according to the invention.

[0030]FIG. 4 is a plan view of a first of the optical waveguide platesforming part of the full mesh optical backplane according to theinvention.

[0031]FIG. 5 is a plan view of a second of the optical waveguide platesforming part of the full mesh optical backplane according to theinvention.

[0032]FIG. 6 is a section view taken along line 6-6 of FIG. 4.

[0033]FIG. 7 is an enlarged perspective view of the mating structures,i.e., electro-optical interface, of the optical backplane according tothe invention.

[0034]FIG. 8 is a plan view showing the orientations of four copies eachof the first and second optical waveguide plates of FIGS. 4 and 5 priorto assembly in the stacked arrangement of FIG. 1, with individual platesor layers marked according to the table of FIG. 3.

[0035]FIG. 9 is a transparent plan view showing the resulting opticalconnectivity, enabled by stacked optical waveguide plates, between allcircuit board assemblies arranged radially about the full mesh opticalbackplane according to the preferred embodiment of the invention.

[0036]FIG. 10 is a schematic illustration of a modified embodiment ofthe invention utilising rectangular optical waveguide plates.

[0037]FIG. 11 is a plan view of an full mesh optical interconnect in theform of a midplane.

[0038]FIG. 12 is a plan view of a combined circular and rectilinear fullmesh optical interconnect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] Referring to FIG. 1 of the drawing, a full mesh opticalinterconnect according to the invention in the form of backplane Icomprises in general assembly a stack of number n, or in this case,eight optical wave guide plates 2, electrical power distribution meansincluding a more positive electrical power supply conductor 3 and a morenegative power supply conductor 4, a cardguide 5 with guide slots 6, 7and 8 for mounting a circuit board assembly 11 (FIG. 2), and opticalwaveguide receiver ports 9 and optical waveguide transmitter ports 10for registry with electro-optical interfaces 13 of FIG. 2. Power supplyconductors 3 and 4 are provided for each cardguide 5 in preferredembodiment.

[0040] In preferred embodiment, the waveguide plates are cylindricaldiscs stacked end to end to form a backplane cylinder. As shown in FIG.1, there are n or eight sets of power distribution means and cardguidesarranged symmetrically along the outer surface of the backplane cylinderand parallel to the backplane cylinder axis. Eight circuit boards arefitted to the cardguides with electro-optical interfaces 13 in opticalregistry with optical waveguide receiver ports 9 and optical waveguidetransmitter ports 10 and with the circuit boards contacting the powerdistribution means. When so assembled, the circuit boards projectradially from the backplane cylinder and those skilled in the art willrecognize that a supporting frame (not shown) may easily be constructedabout this circuit board assembly. The waveguide plates 2 in the stackare more particularly identified by letters a′, b′, c′, d′, e′, f′, g′,and h′. The circuit board assembly card guides 5 are identified byletters a, b, c, d, e, f, g, and h. Letters a through h also identifythe location of eight fixed stations equally spaced about thecircumference of the optical backplane stack.

[0041] A circuit board assembly 11 designed for operation with thepresent invention is illustrated in FIG. 2 wherein the circuit boardcomprises (n−1) or seven electro-optical interfaces 13 in opticalregistry with optical waveguide receiver ports 9 and optical waveguidetransmitter ports 10, and alignment tabs 12 to mate with cardguide slots6, 7, and 8. The illustrated circuit board assembly is shown as it wouldbe used in circuit board cardguide station a. The electro-opticalinterfaces 13 are marked letters a′, b′and d′-h′ to indicate registrywith plates a′, b′ and d′-h′ of the backplane. Those skilled in the artwill recognize that additional surface area is required on the circuitboard assembly 11 to provide space for active circuitry and thatmultiple redundant power contacts can be placed along the edge 11 acontaining the electro-optical interfaces 13 to provide for reliablepower distribution.

[0042] It is to be understood that each circuit board assembly 11 iselectrically isolated from all other circuit board assemblies in thesystem, except for common power connector, it being understood in theart that such power connector can also be electrically isolated.

[0043] Those skilled in the art will recognize that the surface area ofthe backplanes is minimized and less restrictive of air flow thereby tomaximize air cooling of the system.

[0044]FIGS. 4 and 5 respectively illustrate first and second types ofwaveguide plates. The waveguide plate 16 of FIG. 4 is an opaque opticalbody 19 with three pairs 20 of optically transparent side-by-sidewaveguides, with each waveguide pair comprising a receive waveguide 9 inoptical registry with electro-optical interface 13 receiver port 9 a(FIG. 7) and a transmit waveguide 10 in optical registry withelectro-optical interface 13 transmit port 10 a. The optically opaquebody at 19 a (FIG. 6) also extends between the side-by-side transmitwaveguide 10 and the receive waveguide 9 so that the two waveguidemembers of the pair are optically isolated from each other. FIG. 6 showsa cross section of the waveguide plate of FIG. 4 with the transmitwaveguide 10 and the receive waveguide shown to extend only partiallyinto the optically opaque body 19. The diminutive sizes of the transmit10 and receive 9 waveguides is intended to maximize the density of theoptical flux within each waveguide.

[0045]FIG. 7 of the drawing illustrates the mating surfaces for thetransmit 10 and receive 9 waveguides. Recesses are formed to providepositive locating means for the electro-optical interface 13. Thesemating structures also allow for the abutment of another set ofwaveguides that may extend the optical path directly onto the circuitboard assembly 11. A dividing wall 24 prevents light from the transmitwaveguide 10 from entering the receive waveguide 9.

[0046] The second type of waveguide plate 17 is shown in FIG. 5 in whichfour pairs of optical waveguides are provided. Each pair of opticalwaveguides comprises both a transmit waveguide 10 and a receive 9waveguide in side-by-side relationship and optically isolated from eachother along their entire lengths, and optically isolated from each otherat waveguide ports 9 a and 10 a at the perimeter P of the plate 17.

[0047] The first and second waveguide plates of FIGS. 4 and 5 arecircles of the same diameter with cardguide stations a-h equally spacedabout the circumference of the plates. With eight circuit boardassemblies the spacing is 45° between adjacent stations. Thisarrangement provides minimal optical path length, and in consequence,minimizes transmission delays in the optical signals. In three-pairwaveguide plate a′ of FIG. 4, the three waveguides are parallel to eachother, one waveguide of the three is diametrical between stations a-e,two are chords of the circle b-d, f-h, and the remaining diametricallyopposed stations c-g are left blank. This basic waveguide pattern shifts450 with respect to fixed circuit board assembly stations a-h as thepattern is applied to plates b′, c′, and d′ seen in FIGS. 1 and

[0048] In the four waveguide plates e′-h′ (FIGS. 1, 5, and 8), fourparallel waveguides define chords of the circle between fixed circuitboard assembly stations a-h spaced apart 45° on each plate. Theconnectivity pattern shifts 45° as it is applied to plates e′, f′, g′,and h′.

[0049] In FIG. 4, the radially installed circuit board assemblies areindicated by numeral 18.

[0050]FIG. 8 illustrates the set of four three-pair waveguide plates 16referred to specifically to as plate or layer a′ through layer d′, and aset of four four-pair waveguide plates 7 identified as layer e′ throughh′. The waveguide plates 16 and 17 of FIG. 8 contain the requisitetwenty-eight waveguide pairs 15 for the preferred embodiment. The plateidentification letters also appear in sequence a′-h′ in the opticalwaveguide stack of FIG. 1. Each wave guide plate 16 and 17 in FIG. 8 iscircumscribed with cardguide or station letters a through h to indicateparticular cardguide stations with respect to each plate and cardguidestations with respect to each transmit/receive waveguide pair. It willbe further observed in FIG. 8 that waveguide plates a′-d′ and e′-h′ arerotated with respect to each other and assume four different angularpositions. In the preferred embodiment of FIG. 8 the plate to plateangular separation is 45°. It is to be seen then, that the circuit boardassembly 11 in FIG. 2 for card guide a has no electro-optical interface13 at the position of layer c′ because, as shown for layer c′ in FIG. 8,there is no optical waveguide terminus for cardguide at the position oflayer c′. For the same reason, the circuit board assembly e for layer c′omits an electro-optical interface 13 at layer c′, and so forth forlayers a′, b′, and d′.

[0051] Those skilled in the art recognize that there are several methodsof construction to achieve the desired configuration of waveguide plate.For example, the optically opaque body can be machined to form slots forthe transparent waveguide pairs 20. The waveguide pairs also can bemachined to fit. The optically opaque body 19 can be injection moldedleaving voids where the waveguide pairs are to reside with a secondarymolding operation with optically transparent material used to form thewaveguide pairs 20.

[0052] A table showing a matrix of interconnections for theelectro-optical interfaces of eight circuit board assemblies a-h andwaveguide terminuses for waveguide plates a′-h′ is shown in FIG. 3. Forexample, the circuit board assembly installed at optical backplanestation d has electro-optical interfaces in optical registry with thewaveguide receive ports 9 a and transmit ports 10 a of waveguide platesor layers e′, a′, f′, g′, c′, h′, and d′. The diagonal of the tableshows that it is not necessary to connect a circuit board assembly toitself through an optical backplane. The table also shows the orthogonalnature of the interconnection scheme where the matrix portions above andbelow the diagonal are mirror images. This orthogonal symmetryrepresents the paired nature of the interconnect for opticaltransmission and reception.

[0053]FIG. 9 of the drawing depicts a transparent end-on view of thevertically stacked full mesh backplane of the preferred embodimentcircumscribed with letters representing the same cardguide stations ofFIGS. 1 and 8. The twenty-eight pairs of optical waveguides aresuperimposed to illustrate in FIG. 9 that each circuit board assemblya-h is connected to every other circuit board assembly for opticaltransmission and reception through a particular pair of opticalwaveguides.

[0054]FIG. 10 illustrates a modified embodiment of the invention in theform a set of waveguide plates 27 for a rectilinear full mesh opticalbackplane. The rectangular waveguide plates identified as layers a′through h′ include a first set of four three-pair wave guide plates(layers a′-d′) and a second set of four four-pair plates (layers e′-h′)with waveguide pairs 1-5, 2-4, and so forth extending from a common edge27 a of each plate. The principles specified in the preferred embodimentfor power distribution, location of circuit board assemblies,positioning of electro-optical interfaces, optical isolation oftransmit/receive waveguide pairs, and connectivity apply, mutatismutandi, to the embodiment of FIG. 10. In each waveguide plate thecircuit board assembly stations 1-8 are equally spaced on a straightedge 27 a and the four three-waveguide plates as well as the fourfour-waveguide plates have waveguide arcs connecting the severalstations such that when the plates are stacked with stations 1-8 alignedand assembled with circuit boards to form a communications system, eachcircuit board communicates with every other circuit board in theysystem.

[0055] In this alternate embodiment, a more ordinary system constructionis allowed in which the circuit board assemblies are installed parallelto each other as opposed to installation in a circular array.

[0056]FIG. 11 illustrates another embodiment of the invention. Theinvention has thus far been described as an optical backplane. The set37 of waveguide plates of FIG. 11 are used to construct an interconnectdevice sometimes referred to as a midplane which is a backplane withcircuit board assemblies connected to both sides. Midplanes are found insystems where it is undesireable to change a cabling installation onceit has been completed.

[0057]FIG. 11 illustrates a set of four three-pair waveguide platesreferred to specifically to as plate or layer a′ through layer d′, and aset of four four-pair waveguide plates identified as layer e′ throughh′. The waveguide plates of FIG. 11 contain the requisite twenty-eightwaveguide pairs for this midplane embodiment. Each waveguide plate inFIG. 11 is circumscribed with cardguide or station letters 1 through 8to indicate particular cardguide stations with respect to each plate andcardguide stations with respect to each transmit/receive waveguide pair.It will be further observed in FIG. 11 that waveguide plates a′-d′ ande′-h′ are stacked with respect to each other and present two sides 37a-b and 37 c-d for receiving circuit board assemblies.

[0058] The midplane of FIG. 11 is an improvement on an electricalmidplane because there is no need to stagger the electrical connectorlocations as those skilled in the art recognize. Additionally, it is tobe recognized that using additional waveguide plates carrying additionalwaveguides from the generally frontmost side to the generally rearmostside may be useful as a means of simple optical isolation frominput/output circuitry which may be exposed to high voltages or highenergy surges.

[0059]FIG. 12 shows in plan view a system utilizing an opticalinterconnection scheme comprising sections of rectilinear 47 andcircular 57 midplanes. Such construction may be useful when highbandwidth circuit board assemblies need a short and fast communicationpath such as is provided by a circular midplane while other circuitboard assemblies can use the generally longer communications pathsprovided by a rectilinear midplane wherein the overall system mustreside in a typical rack-mounted enclosure.

[0060] In FIG. 12, the circular and rectangular sections of the midplaneare connected simply by abutting some interconnecting waveguides betweenthe two otherwise independent sections. The pairs of rectilinear 47 andcircular 57 waveguide plates referred to specifically as plate or layera′ through layer d′, and as layer e′ through h′. The waveguide plates 47and 57 contain the requisite n−1 waveguide pairs for each of n circuitboard assemblies with this midplane illustrative embodiment having eightcircuit board assemblies. Each wave guide plate 47 and 57 in FIG. 12 iscircumscribed with cardguide or station letters 1 through 8 to indicateparticular cardguide stations with respect to each plate and cardguidestations with respect to each transmit/receive waveguide pair, with acorresponding number (n−1) of optically isolated transmit and receivewaveguide paths. It will be further observed in FIG. 12 that waveguideplates a′-d′ and e′-h′ are stacked with respect to each other andpresent circular and rectilinear surfaces for receiving circuit boardassemblies.

[0061] The rectilinear plates 47 are characterized by straight edges 47a-b joined by curvilinear edge 47 c preferably being circular. Thecurvilinear plates 57 are preferably circular and abut correspondingedge 47 c of plate 47. When nested, plate e′ for example, providescommunication paths in the form of waveguides 6-7, 5-8, 1-4, and 2-3.

[0062] Those skilled in the art will see that any connectivity can beestablished for any number of circuit board assemblies by takingadvantage of the present invention.

[0063] The present invention lends itself very well to the notions ofredundancy and fault tolerance. Since it is contemplated that thewaveguide plates or layers are relatively thin, the height of an opticalinterconnect for a given number of circuit board assemblies would berather small. Consequently, a fully redundant backplane can easily bemade to fit in most systems so that an additional set of communicationspaths is always readily available should a component associated with oneor more of those in use fail. Alternatively, the additionalcommunications paths can be used to handle any additional bandwidthshould a given system require it. This additional bandwidth may comefrom the mere addition of communications paths or it may come from theconstruction of a logical bus or wide data path between circuit boardassemblies. An additional capability provided by such simplescaleability is that in some systems it is desirable to provideseparation of the transmitter and the receive circuitry for ease ofcircuit board assembly layout and to minimize any interference that highpower transmitters may introduce into high sensitivity receivers.

[0064] The waveguide plates 16, 17, 27, 37, 47 and 57 are described indetail above for transmit and receive optical signals in the opticallyisolated side-by-side waveguide paths. It is to be understood the theside-by-side waveguide paths are capable of conducting transmit andtransmit optical signals as well as receive and receive optical signals.

[0065] Various changes may be made to the structure embodying theprinciples of the invention. The foregoing embodiments are set forth inan illustrative and not in a limiting sense. The scope of the inventionis defined by the claims appended hereto.

We claim:
 1. An optical interconnect for an electronic system comprisinga plurality of waveguide plates arranged in a stack, a number (n)circuit board assemblies mounted on the stack, redundant powerdistribution means for each circuit board assembly, the stack ofwaveguide plates having an aggregate number w of optically isolatedtransmit and receive waveguide paths, where w=((n)×(n−1)/(2)), eachcircuit board having a number (n−1) of electro-optical interfaces inoptical registry with transmit and receive paths whereby each circuitboard assembly communicates with every other circuit board assembly inthe system.
 2. An optical interconnect for an electronic systemcomprising a plurality of waveguide plates arranged in a stack, a number(n) circuit board assemblies mounted on the stack, redundant powerdistribution means for each circuit board assembly, the stack ofwaveguide plates having an aggregate number w of optically isolatedtransmit and receive waveguide paths, where w=((n)×(n−1)/(2)), eachcircuit board having a number (n−1) of electro-optical interfaces inoptical registry with transmit and receive paths whereby each circuitboard is electrically isolated from every other circuit board assemblyin the system.
 3. A waveguide plate as defined in claim 2 which iscircular to minimize the length of optical paths and thereby to minimizetransmission delays.
 4. A waveguide plate as defined in claim 2 which isrectilinear.
 5. A waveguide plate as defined in claim 2 which isrectilinear and circular.
 6. An optical interconnect for an electronicsystem comprising a plurality of waveguide plates arranged in a stack, anumber (n) circuit board assemblies mounted on the stack, redundantpower distribution means for each circuit board assembly, the stack ofwaveguide plates having an aggregate number w of optically isolatedtransmit and receive waveguide paths, where w=((n)×(n−1)/(2)), eachcircuit board having a number (n−1) of electro-optical interfaces inoptical registry with transmit and receive paths whereby circuit boardsurface area is minimized for optimum air cooling of the system.
 7. Awaveguide plate comprising at least one pair of side-by-side opticallyisolated paths passing through the body with the optical paths beingoptically accessible at spaced pairs of adjacent optically isolatedports at the surface of the body.
 8. A waveguide plate as defined inclaim 7 in which the paths and ports accommodate transmit and receiveoptical signals.
 9. A waveguide plate as defined in claim 7 in which thepaths and ports accommodate transmit and transmit optical signals.
 10. Awaveguide plate as defined in claim 7 in which the paths and portsaccommodate receive and receive optical signals.
 11. A waveguide platefor an optical interconnect comprising a plurality of pairs ofside-by-side optically isolated transmit and receive paths passingthrough the body with the optical paths being optically accessible atspaced pairs of adjacent optically isolated receive and transmit portsat the surface of the body.
 12. An optical interconnect in the form of amidplane for an electronic system having a plurality of circuit boardassemblies with electro-optical interfaces, the interconnect comprisinga set of waveguide plates having a plurality of waveguide pairsextending between front and back edges of the plates, the waveguidepairs terminating in optically isolated waveguide ports definingcardguide stations at the front and back edges, the waveguide platesbeing stacked with respect to each other and presenting the front andback edges for receiving the electro-optical interfaces of the circuitboard assemblies at the cardguide stations.
 13. An optical interconnectfor an electronic system comprising eight waveguide plates arranged in astack, eight circuit board assemblies mounted on the stack at 45°stations about the stack, redundant power distribution means for eachcircuit board assembly, the stack of waveguide plates having fourthree-pair plates of side-by-side optically isolated transmit andreceive paths passing through the body, the three pair of paths in eachplate being parallel to each other with one path extending diametricallyof the plate between stations, and two paths extending as chords betweenstations, and the paths being optically accessible at spaced pairs ofadjacent optically isolated receive and transmit ports at the stationson the plate the stack of waveguide plates further having four four-pairof side-by-side optically isolated transmit and receive paths passingthrough the body, the four pair of paths being parallel to each otherand extending as chords between stations, and the paths being opticallyaccessible at spaced pairs of adjacent optically isolated receive andtransmit ports at the stations on the plate thereby providing anaggregate of twenty-eight optically isolated transmit and receivewaveguide paths, each circuit board having seven of electro-opticalinterfaces in optical registry with transmit and receive paths wherebyeach circuit board assembly communicates with every other circuit boardassembly in the system.
 14. An optical interconnect for an electronicssystem comprising a plurality of waveguide plates arranged in a stack, anumber (n) of circuit board assemblies mounted on the stack at spacedstations, redundant power distribution means for each circuit boardassembly, the stack of waveguide plates having a number (n/2) of(n−2)/2)-pair plates of side-by-side optically isolated transmit andreceive paths passing through the body, and the paths being opticallyaccessible at spaced pairs of adjacent optically isolated receive andtransmit ports at the stations on the plate; the stack of waveguideplates further having a number ((n)/(2)) of (n)/2-pair of side-by-sideoptically isolated transmit and receive paths passing through the body,the paths being optically accessible at spaced pairs of adjacentoptically isolated receive and transmit ports at the stations on theplate thereby providing an aggregate number ((n)×(n−1)/(2)) of opticallyisolated transmit and receive waveguide paths, each circuit board havinga number (n−1) of electro-optical interfaces in optical registry withtransmit and receive paths whereby each circuit board assemblycommunicates with every other circuit board assembly in the system. 15.An optical interconnect as defined in claim 14 in which the waveguideplates are circular.
 16. An optical interconnect as defined in claim 14in which the waveguide plates are rectilinear.
 17. An opticalinterconnect as defined in claim 14 in which the waveguide plates arerectilinear and circular.
 18. A waveguide plate for an optical backplanecomprising at least one pair of side-by-side optically isolated transmitand receive paths passing through the body with the optical paths beingoptically accessible at spaced pairs of adjacent optically isolatedreceive and transmit ports at the surface of the body, the receive andtransmit ports being recesses defining positive locating means for anelectro-optical interface and for receiving another set of waveguides toextend the optical paths directly onto a circuit board assembly.
 19. Anoptical interconnect in the form of a midplane for an electronic systemhaving a plurality of circuit board assemblies with electro-opticalinterfaces, the interconnect comprising rectilinear and circularmidplane sections, the rectilinear section having front and back edgesand a concave circular edge interconnecting the front and back edges,the rectilinear sections defining a set of waveguide plates having aplurality of waveguide pairs extending between front, back and circularedges of the plates, the circular sections defining a set of waveguideplates having a plurality of waveguide pairs extending between circularedges of the plates, the rectilinear and circular sections being nestedwith the circular sections abutting the concave edge of the rectilinearsections, the waveguide pairs of rectilinear and circular sectionsterminating in optically isolated waveguide ports defining cardguidestations at the front, back, and circular edges, the waveguide platesbeing stacked with respect to each other and presenting the front, backand circular edges for receiving the electro-optical interfaces of thecircuit board assemblies at the cardguide stations.
 20. An opticalbackplane to provide communications paths for electronics systems withelectro-optical interfaces, the backplane comprising a plurality ofwaveguide plates having at least one pair of side-by-side opticallyisolated transmit and receive paths passing through the plates with theoptical paths being optically accessible at spaced pairs of adjacentoptically isolated receive and transmit ports at the surface of theplates, the receive and transmit ports defining means for receivingelectro-optical interfaces whereby a fully redundant backplane fits inelectronic systems so that an additional set of communications paths isavailable should an electronics system communications path in use fail.21. An optical interconnect for an electronic system having any numberof circuit board assemblies, the interconnect comprising at least onewaveguide plate in the form of an opaque body having three pair ofside-by-side optically isolated transmit and receive paths passingthrough the body, and at least one waveguide plate in the form of anopaque body having four pair of side-by-side optically isolated transmitand receive paths passing through the body.
 22. An optical interconnectfor an electronic system having any number of circuit board assemblies,the interconnect comprising a plurality of stacked waveguide plateshaving internal, optically isolated communication paths accessible atthe surface of the plates to any number of circuit board assemblies, thewaveguide plate stack having an end surface to which additionalwaveguide plates may be added for serving new circuit board assembliesadded to the system thereby to upgrade the system without the need for aforklift upgrade.